Size-Resolved Characterization of Particle Hydroxymethanesulfonate (HMS), Sulfite, Bisulfite, and Sulfate in Wintertime Fairbanks, Alaska

KAYANE DINGILIAN, Elliana Hebert, Michael Battaglia, James Campbell, Jingqiu Mao, Rodney J. Weber, Georgia Institute of Technology

     Abstract Number: 423
     Working Group: Aerosols Spanning Spatial Scales: Measurement Networks to Models and Satellites

Abstract
Previous analysis of online and offline measurements of particulate matter during the ALPACA campaign of January-February 2022 in Fairbanks, Alaska identified significant levels of the S(IV) species hydroxymethanesulfonate (HMS), sulfite, and bisulfite, and the S(VI) species sulfate. Recent analysis of samples collected with a nine-stage Microorifice Uniform Deposit Impactor (MOUDI) show a strong dependence of the fraction of HMS in total S(IV) on particle size. HMS (organic S(IV)) dominates the fine mode (PM2.5) and sulfite and bisulfite (together termed “inorganic S(IV)”) dominate the coarse mode (PM >2.5). The total S(IV)/sulfate fraction also has a distinct trend, with the ratio above unity in the coarse mode and below half in the fine mode, possibly indicative of primary sources of inorganic S(IV). The data were categorized into three periods – the main pollution event (late Jan-early Feb), a contrasting clean period (mid Feb), and a period of intermediate total S(IV) levels (mid Jan). For all three periods, the total S(IV) distribution is bimodal, with a heightened relative contribution of HMS to total S(IV) in the fine mode during the intermediate and main pollution events. This suggests that HMS chemistry may not be the sole fate of aqueous inorganic S(IV) even in a formaldehyde-rich environment. We are investigating the possibility of additional physical and chemical factors enhancing or inhibiting HMS formation, such as particle liquid water content, diffusion and transport, precursor solubility and uptake, metal complexation, etc. Overall, size-resolved measurements of HMS, inorganic S(IV), and sulfate provide insights into the unique sulfur chemistry occurring in cold urban environments.